As a structure for supporting a unit case, which includes a gear housing which houses a gear train and a shaft housing which houses a drive shaft, on a vehicle body frame, there has been, for example, a structure as illustrated in FIG. 10. In this conventional technology, support members B are rotatably fitted to shaft housings A, respectively, and thereafter, the support members B are connected to a vehicle body frame C so that a unit case D is supported by the vehicle body frame C. A pillar-shaped link portion F is provided on the support member B so as to protrude toward a gear housing E. A bolt H is screwed into the link portion F through a reaction force receiving portion G of the gear housing E so that the link portion F can prevent relative rotation between the unit case D and the vehicle body frame C about a shaft center of a drive shaft J (see, for example, Patent Literature 1).